Compositions: coating or plastic – Coating or plastic compositions – Coating repellent
Reexamination Certificate
2002-09-27
2003-11-25
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Coating repellent
C101S451000
Reexamination Certificate
active
06652631
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a dampening water composition for a lithographic printing plate, and more specifically, to a dampening water composition which is useful for offset printing using a lithographic printing plate. The present invention also relates to a lithographic printing process.
BACKGROUND OF THE INVENTION
The lithographic printing technique makes the best use of the properties of water and oil such that they are essentially incompatible with each other. Two different areas are formed on the printing surface of a lithographic printing plate, one receiving water and repelling oil ink and the other repelling water and accepting the oil ink. The former serves as a non-image area and the latter becomes an image area.
The non-image area is made damp with a dampening water for use in lithographic printing in practice, thereby increasing the difference in surface chemical properties between the image area and the non-image area. Both the ink repellency of the non-image area and the ink receptivity of the image area can be thus increased.
The conventionally known dampening water are aqueous solutions of, for example, alkali metal salts or ammonium salts of bichromic acid, phosphoric acid or salts thereof such as ammonium salt, and a colloidal substance such as gum arabic or carboxymethyl cellulose (CMC). However, it is difficult to uniformly dampen all the non-image areas formed on the lithographic printing plate with the above-mentioned conventional dampening water, and for this reason, the resultant printed matters sometimes get smudged. In addition, a high degree of skill is required to control the amount of dampening water supplied to the printing plate.
To overcome such problems, the Dahlgren dampening system has been introduced, which employs as a dampening water an aqueous solution containing about 20 to 25% of isopropyl alcohol. This method provides some advantages, for example, an improvement in workability and an increase in the accuracy of obtained printed matters. To be more specific, the wettability of the non-image area with the damping water is improved so that the amount of the dampening water to be applied can be reduced. The result is that the balance between the amount of the printing ink and that of the dampening water to be supplied can be easily controlled, and that the amount of water to be emulsified into the printing ink can be lowered, thereby improving the transfer performance of the printing ink to the blanket.
However, isopropyl alcohol used in the Dahlgren dampening system evaporates easily and quickly, and therefore, a special device for keeping the predetermined concentration of isopropyl alcohol in the dampening water is required. This is unfavorable from the viewpoint of cost. Moreover, the Dahlgren dampening system is disadvantageous in terms of working environment because isopropyl alcohol gives out a disagreeable smell and produces a problem of toxicity.
Even if such a dampening water containing isopropyl alcohol is applied to conventional offset printing in which a dampening molleton roller is used, no effect can be obtained because isopropyl alcohol easily evaporates from the roller surface and the printing plate surface.
Moreover, the pollution by industrial waste has recently become a matter of public concern. There is a tendency that the discharge of chromium ions from the conventional dampening water into waste water is severely regulated and the use of organic solvents such as isopropyl alcohol is controlled in light of safety and hygiene.
Accordingly, a dampening water composition containing no isopropyl alcohol or reduced amount of isopropyl alcohol has been desired for the lithographic printing plate. For example, JP KOKOKU Nos. Sho 55-25075, Sho 55-19757 and Sho 58-5797 disclose dampening water compositions comprising a variety of surfactants. However, when such dampening water compositions are used in practice, it is necessary to control the concentration of the surfactant in each dampening water composition to a considerably high level for obtaining the dampening water composition with a surface tension of 35 to 50 dyn/cm. In addition, the above-mentioned dampening water compositions containing a variety of surfactants cannot completely solve the problem that water is attached to an ink layer and ink is dispersed in the surface portion of a water layer, which problem results from vigorous motion of both ink and water under the conditions that the ink roller, printing plate, and dampening water feeding roller are rotated at high speed in the course of lithographic printing. These dampening water compositions have still another shortcoming that foaming is easily caused while the dampening water compositions are pumped up and stirred.
U.S. Pat. Nos. 3,877,377 and 4,278,467 and JP KOKAI No. Sho 57-199693 disclose dampening water compositions comprising some solvents other than isopropyl alcohol. Such dampening water compositions are considered to be advantageous in terms of safety and hygiene in light of the absence of isopropyl alcohol. However, when these dampening water compositions are used together with a lithographic printing plate which comprises an anodized aluminum plate as a substrate, the non-image area is contaminated with ink during printing, which is called “scumming”, and the configuration of dot-image becomes abnormal, to be more specific, the dots become larger than a predetermined size and uneven as a whole, which problem is called “fill-in”. Moreover, the use of such dampening water compositions free from isopropyl alcohol imposes limitations on the kind of printing press to be used. The isopropyl alcohol free system cannot be achieved in the Dahlgren dampener system and a commercially available dampener system “Alcolor” (trademark), made by Heidelberger Druckmaschinen AG.
JP KOKOKU No. Sho 64-7599 proposes to use a desensitizing solution containing acetylene glycol for the lithographic printing plate. However, such a desensitizing solution cannot exhibit the stable continuous printability for an extended period of time.
In recent years, soybean oil ink that uses soy bean oil as a solvent has been widely introduced into both the sheet-feed press and the rotary offset in consideration of environment protection and conservation of petroleum resources. While linseed oil conventionally used in this field is a drying oil, the soy bean oil is a semi-drying oil, so that the drying properties of the soybean oil ink after printing operation are unsatisfactory. Insufficient drying properties of the soybean oil ink produce the problems of offset and blocking.
Accordingly, a dampening water composition for the lithographic printing plate capable of producing printed matters with high quality has been desired, which dampening water composition is safe from the viewpoint of environmental hygiene, which does not require any technical skill when used in printing operation so that the supply amount of dampening water can be adjusted with no difficulty, and which is applicable to any printing press, and which can exhibit such excellent dampening water properties as to prevent the contamination of the printing plate and cope with high speed printing.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a dampening water composition for the lithographic printing plate capable of producing excellent printed matters, which dampening water composition can replace the isopropyl alcohol based dampening water composition so as to provide a comfortable and safe working environment. Another object of the present invention is to provide a dampening water composition having such a low dynamic surface tension that stable continuous printability can be ensured even under the conditions that the surrounding members are rotated at high speed. A further object of the present invention is to provide a dampening water composition which can exhibit excellent printability in any kinds of printing presses.
Under such circumstances, the inventor of this invention has conducted various studies on a d
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Klemanski Helene
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